An autoinjector is a small, single-use syringe designed to administer a set dosage of medicine rapidly. They are designed for untrained usage or self-administration, being simple to use and having a preset dosage contained within, reducing the risk of accidental overdose or introduction of bubbles into the bloodstream. Most autoinjectors are spring-loaded syringes, though some are jet injectors (i.e., they use the force of a concentrated stream of liquid to pierce the skin rather than a hypodermic needle).